The purpose of the present invention is to increase the efficiency of the sound absorption of the engine over the known constructions by considerably reducing the air intake noise at the air filter compared with comparable types of structures. This purpose is inventively attained by the air filter having a separate flat ring housing for the combustion air and being arranged within the inlet channel and by the air inlet into the ring housing of the air filter taking place through a funnellike pipe which extends preferably parallel to the cylinder axis into the inside of the casing. In this manner, the sound oscillations which start out from the air filter encounter prior to their exit from the engine casing many obstacles and passageways which reduce the noise level, such as multiple deflections and reflections, and passage thereof through chambers of differing volumes, which chambers lie one behind the other, passages and narrow points and furthermore double wall construction for the guide channels at exposed points and over as much as possible long extents.
A multiple deflection and reflection of the sound waves which start out from the intake port to the air filter is achieved in a very advantageous manner by surrounding the funnellike pipe to the air filter at its port with a depressionlike shielding member. This shielding member is designed according to a different characteristic of the invention as a semi-round sheet-metal part, which is secured on the crankshaft housing and is open toward the adjacent wall of the casing.
It is furthermore very advantageous if the length of the funnellipe pipe is a multiple of its inside diameter.